The unique epitaxial layer characteristics needed for an acoustic charge transport (ACT) device operation must be preserved throughout the course of fabricating integrated circuit elements on the epitaxial layer. This represents a clear and critical distinction between an ACT integrated circuit (ACTIC) and a conventional GaAs integrated circuit fabricated on epitaxial wafers.
In the conventional gallium arsenide integrated circuit fabrication, epitaxial material is used solely as a high-purity substrate for the subsequent introduction of active layers, e.g. by ion implantation, and plays no role in the operation of produced device. In this case, preservation of the characteristics of the starting material is not likely to occur and is furthermore irrelevant. On the other hand, in an ACTIC, the epitaxial material is an active component of the device, and must not be deleteriously affected by the processing required to produce ancillary circuit elements. Moreover, standard gallium arsenide (GaAs) processing will not work in an ACTIC because of the active nature of the epitaxial material, and because of the special requirements of the ACT device which is at the core of the ACTIC.